U.S. Pat. No. 5,509,275 issued Apr. 23, 1996 to Bhatti, et al., and co-assigned to the assignee of the subject invention, discloses a system for continually dehumidifying ambient air that is drawn into a heating, ventilating and air conditioning (HVAC) system of a motor vehicle. Typically, hot air which is also quite humid is simply pulled directly in and forced over a cold evaporator core, which cools the air as well as condensing water out of the air. While drier air enters the passenger cabin, relying upon condensation by the evaporator core brings its own problems, especially microbial growth and its attendant odor. The patent noted provides a desiccant wheel of novel design that continually turns, at slow speed, within the HVAC housing, removing moisture in desiccant lined tubes in an adsorption half of the wheel, which are regenerated in a heated half of the wheel through which hot air is forced. The two "halves" of the wheel are defined by stationary rubbing seals. The tubes run axially from face to face of the wheel, but are not tightly packed, leaving space between for a radial cross flow of outside air that is blown over the outside of the tubes, in both halves of the wheel. The radial cross flow cools the tubes in the adsorption half of the wheel, removing the latent heat released by the desiccant when it adsorbs moisture. The cooling of the tubes in the adsorption half of the wheel is beneficial, since the heat released by the working desiccant is thereby prevented from reaching the evaporator core.
However, the same cross flow, when it crosses the other half of the wheel, is cooler than the heated air simultaneously passing through the inside of the tubes to regenerate the desiccant. Therefore, the cross flow air can potentially reduce the efficiency of the concurrent regeneration process as it passes through the other half of the wheel. In addition, much of the limited volume of the wheel is the empty space necessarily left between the tubes. Since space is at a premium in any HVAC housing, more complete utilization of the volume within the wheel would be desirable.